Thermal Phenomena Resulting in Adhesion and Detachment
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The work herein is devoted to the experimental and theoretical study of adhesion and detachment due to heating. Specifically, adhesion and heat-transfer of polymer compound nonwoven fiber mats and bubble growth and detachment in pool boiling is explored. In the case of thermal-bonding of compound nonwovens, various industrially important questions are addressed such as the optimal temperature and heating conditions required to heat these compound nonwovens, the choice of binder fibers, polymer-polymer interactions during heat-treatment, and morphological changes and the micro-mechanics of fiber binding due to heating. A theoretical model presented in this work describes the transient temperature profile across nonwoven mats during forced air convective heating. This model is then applied to various industrially relevant heating scenarios of interest. Parts of this thesis are also devoted to the experimental study of adhesion and its effect in nonwovens and mixed polymer thin films. For the case of mixed polymer films, it is shown that partial mixing between dissimilar polymers such as polycaprolactone and nylon-6 occurs and significantly affects the adhesion energy. In the second part of the thesis, work on bubble growth and detachment in pool-boiling is studied experimentally and theoretically. It is demonstrated that vaporization fronts propagate with exponentially increasing velocity along heaters in a run-away matter, shedding light on the transition to the critical heat flux. In the case of sub-cooled boiling induced vibrations, it is shown that bubble growth and detachment induces a localized hydrodynamic flow and as a result, vibration of heated surfaces.